Wednesday, 31 January 2024
Hall E (The Baltimore Convention Center)
Coherent eddies and turbulence in the stratocumulus-topped atmospheric boundary layer (ABL) drive processes that determine important large-scale properties of clouds and their effect on climate. The diurnal cycle of stratocumulus clouds is well observed, but turbulent entrainment and decoupling remain poorly modeled because of gaps in understanding of the processes that give rise to them.
High-resolution observations made during 27 days of the VOCALS-REx campaign reveal the diurnal evolution of the properties of tropical marine stratocumulus clouds. Doppler radar and lidar directly measure turbulence, and, when combined with complementary in situ and remotely sensed observations, these data add to our understanding of the processes that control the structure, transitions, and radiative properties of stratocumulus clouds. Analysis of the observational data provides suggested parameterizations and new understanding of turbulence in the ABL.
We approach studying turbulence throughout the stratocumulus-topped ABL via simplified turbulent kinetic energy (TKE), heat, and moisture budgets. Turbulence exhibits a diurnal cycle with an increase during the night hours and decrease during the day, particularly in the cloud layer. Kinematic decoupling between the stratocumulus cloud layer and surface mixed layer during the day and a rapid recoupling accompanied by turbulent mixing in the early evening is suggested by vertical profiles of buoyancy flux. Buoyancy fluxes, inferred from radiative fluxes and heat balance, are negative at cloud base during daylight with a sudden switch to positive at ~1600 LT, indicative of recoupling, that persists throughout the night. The mean estimated turbulent entrainment rate diurnal cycle is consistent with that of cloud-top turbulence, with a minimum occurring at midday and an early evening maximum that follows the rapid recoupling of the boundary layer. Improvements in description and understanding of entrainment and decoupling in the stratocumulus-topped ABL will result in advances in representation of marine low cloud properties in theoretical, weather, and climate models.
High-resolution observations made during 27 days of the VOCALS-REx campaign reveal the diurnal evolution of the properties of tropical marine stratocumulus clouds. Doppler radar and lidar directly measure turbulence, and, when combined with complementary in situ and remotely sensed observations, these data add to our understanding of the processes that control the structure, transitions, and radiative properties of stratocumulus clouds. Analysis of the observational data provides suggested parameterizations and new understanding of turbulence in the ABL.
We approach studying turbulence throughout the stratocumulus-topped ABL via simplified turbulent kinetic energy (TKE), heat, and moisture budgets. Turbulence exhibits a diurnal cycle with an increase during the night hours and decrease during the day, particularly in the cloud layer. Kinematic decoupling between the stratocumulus cloud layer and surface mixed layer during the day and a rapid recoupling accompanied by turbulent mixing in the early evening is suggested by vertical profiles of buoyancy flux. Buoyancy fluxes, inferred from radiative fluxes and heat balance, are negative at cloud base during daylight with a sudden switch to positive at ~1600 LT, indicative of recoupling, that persists throughout the night. The mean estimated turbulent entrainment rate diurnal cycle is consistent with that of cloud-top turbulence, with a minimum occurring at midday and an early evening maximum that follows the rapid recoupling of the boundary layer. Improvements in description and understanding of entrainment and decoupling in the stratocumulus-topped ABL will result in advances in representation of marine low cloud properties in theoretical, weather, and climate models.
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